I've been looking at foam speakers, and then realized something: It would just be easier to make a foam mould, pour in something, and then use acetone to melt out the foam. (It's an old R/C modeller's trick I picked up).
A hot-wire cutter means that cutting foam any way you like is remarkably easy - complex and curved shapes, too. (It's about as easy as drawing on something with a ballpoint pen, if you've got it set up properly.)
Concrete is, however, obscenely heavy, and I want to be able to move my speakers without a forklift.
This brought me to pumice-crete, which seems to be a mixture of concrete and pumice. (Big surprise.) Pumice should work fine for dampening speakers, and it's cheap.
Any thougts?
A hot-wire cutter means that cutting foam any way you like is remarkably easy - complex and curved shapes, too. (It's about as easy as drawing on something with a ballpoint pen, if you've got it set up properly.)
Concrete is, however, obscenely heavy, and I want to be able to move my speakers without a forklift.
This brought me to pumice-crete, which seems to be a mixture of concrete and pumice. (Big surprise.) Pumice should work fine for dampening speakers, and it's cheap.
Any thougts?
Spasticteapot said:
I seem to be following you around today.
A little gasoline goes a long way on polystyrene. You can also oil the polystyrene as a release agent.
Perlite (is that pumice?) is commonly mixed with concrete and will work well but don't forget to use some mesh wire as a rebar scrim. Lighweight concrete is not near as strong.
Concrete mix
tvi,
I have been looking for a better way to increase the strength of my planned 4.6 ft3 concrete spheres (heavy reinforced steel, poly additives, ground rubber, foam beads, etc) and trying to reduce the total weight down from an unreasonable 80 odd Kg to about 50 Kg and this hemp fibre sounds promising. Can you advise on the supplier of hemp fibre here in Melbourne so I can give this a try? As you appear to have done some work in concrete, could I "pick your brains" (!) a bit?
Still under moderation, unfortunately ... James Hill
tvi,
I have been looking for a better way to increase the strength of my planned 4.6 ft3 concrete spheres (heavy reinforced steel, poly additives, ground rubber, foam beads, etc) and trying to reduce the total weight down from an unreasonable 80 odd Kg to about 50 Kg and this hemp fibre sounds promising. Can you advise on the supplier of hemp fibre here in Melbourne so I can give this a try? As you appear to have done some work in concrete, could I "pick your brains" (!) a bit?
Still under moderation, unfortunately ... James Hill
Re: Re: Re: Pumice-crete or other concrete-mix speakers?
A) The Romans invented lightweight concrete, using pumice from Mt Vesuvius.
B) http://www.youtube.com/watch?v=YL3Qy97YXG0
Spasticteapot said:
A) The Romans invented lightweight concrete, using pumice from Mt Vesuvius.
B) http://www.youtube.com/watch?v=YL3Qy97YXG0
My take on this would be to place the concrete where it will do the most good. I'm considering (only dreaming??) using concrete as a back baffle against which to brace the drivers. I can cast a big slug of concrete. I don't want to take you OT, but I'd rather work in wood to hold the drivers...and show them off.
Using one material for everything in a structure brings with it unwanted baggage. Concrete => weight
Weight reduction requires using the concrete only where it is most needed. Same with reinforcing. Place "what is needed" "where it is needed".
If some sketches are available maybe more meaningful suggestions can be made.
For examples of thin-section concrete, search "concrete canoe"
Using one material for everything in a structure brings with it unwanted baggage. Concrete => weight
Weight reduction requires using the concrete only where it is most needed. Same with reinforcing. Place "what is needed" "where it is needed".
If some sketches are available maybe more meaningful suggestions can be made.
For examples of thin-section concrete, search "concrete canoe"
Thank for the input -
Foamed concrete, Hebel, pumice, Perlite (kitty litter). foam beads, aerated (air bubbles), reduced ettrigite (added Silica, fly ash, etc ), surfacants, mesh reo, cure rates, canoe and yacht techniques (thanks Ed) - very interesting indeed
About the weight business - you need a RIGID chamber to elimenate vibrations from radiating ANY energy from the Baffle, Sides, Top/bottom, and especially the Rear into your room plus a method of stopping the chamber itself from viabrating .(Constrained Layer Damping [CLD], etc),
So, for a 12" driver producing about 110dB output (easily at 97dB/w) plus another 15 dB for transients, you need about 95 lbs mass for 15hz (1/2 lower freq of 30 hz), EXCLUDING the Support stand damping/coupling effects. Now, things are not usually this demanding because the power required below 40hz is generally much lower (but not always), so this is why the mass factor is reduced to 95 lbs apparently.
I can understand the reasoning but got lost in the calculations some time ago, but this seems to be the accepted mass to pressure value in pro-audio circles.
Then, the business of Constrained Layer Damping has to be added to the design - there are some different opinions about this absorbtion (or not) of the internal energy and at what rate, et. This is fairly well understood and for most of us, is just a matter of application - additions to the concrete mix, shape and reinforcing, damping layers, etc.
When you add the effects of the damping/ freq response of the stand, then flat pwr and freq response is quite possible down very low indeed and sounds very good indeed! (much better!)
Enter the dreaded spectre of ROOM ACOUSTICS!
I have never understood (?) the refusal of the domestic audio industry to accept the "room" as part of the Audio Sound System.
One of the sites that is a MUST SEE is the "Room Tunes" and other "Room Acoustics" websites and from there the whole business of taking control of your boom/room (approx 30 - 40% of your sound!) is getting used to the ideas and simple projects.
.
It's no big suprise how a bit of mucking about with cheap common materials can give such amazing improvements in your room - the big suprise is why so few people actually do it instead of continually changing their equiptment.
I'm a nut about good, clean, accurate sound and it's been fairly straightforward to sort out this temporary 18' x 16' x 10' disaster of a room, and when the new Ridgid base chambers are finished, no doubt some further "mucking about" will be required to get the room right again.
It's a suprise how well the Passlab designs like silver interconnect; but that's another story!
Thank you all for your input - it's great!
Yrs ... jh
Foamed concrete, Hebel, pumice, Perlite (kitty litter). foam beads, aerated (air bubbles), reduced ettrigite (added Silica, fly ash, etc ), surfacants, mesh reo, cure rates, canoe and yacht techniques (thanks Ed) - very interesting indeed
About the weight business - you need a RIGID chamber to elimenate vibrations from radiating ANY energy from the Baffle, Sides, Top/bottom, and especially the Rear into your room plus a method of stopping the chamber itself from viabrating .(Constrained Layer Damping [CLD], etc),
So, for a 12" driver producing about 110dB output (easily at 97dB/w) plus another 15 dB for transients, you need about 95 lbs mass for 15hz (1/2 lower freq of 30 hz), EXCLUDING the Support stand damping/coupling effects. Now, things are not usually this demanding because the power required below 40hz is generally much lower (but not always), so this is why the mass factor is reduced to 95 lbs apparently.
I can understand the reasoning but got lost in the calculations some time ago, but this seems to be the accepted mass to pressure value in pro-audio circles.
Then, the business of Constrained Layer Damping has to be added to the design - there are some different opinions about this absorbtion (or not) of the internal energy and at what rate, et. This is fairly well understood and for most of us, is just a matter of application - additions to the concrete mix, shape and reinforcing, damping layers, etc.
When you add the effects of the damping/ freq response of the stand, then flat pwr and freq response is quite possible down very low indeed and sounds very good indeed! (much better!)
Enter the dreaded spectre of ROOM ACOUSTICS!
I have never understood (?) the refusal of the domestic audio industry to accept the "room" as part of the Audio Sound System.
One of the sites that is a MUST SEE is the "Room Tunes" and other "Room Acoustics" websites and from there the whole business of taking control of your boom/room (approx 30 - 40% of your sound!) is getting used to the ideas and simple projects.
.
It's no big suprise how a bit of mucking about with cheap common materials can give such amazing improvements in your room - the big suprise is why so few people actually do it instead of continually changing their equiptment.
I'm a nut about good, clean, accurate sound and it's been fairly straightforward to sort out this temporary 18' x 16' x 10' disaster of a room, and when the new Ridgid base chambers are finished, no doubt some further "mucking about" will be required to get the room right again.
It's a suprise how well the Passlab designs like silver interconnect; but that's another story!
Thank you all for your input - it's great!
Yrs ... jh
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